Chapter 8: Sampling Distributions

Consider the following three news items.

The average price of unleaded regular fell by 1.6 cents to $3.667 a gallon on Saturday, from $3.683 a gallon, according to survey results from the motorist group AAA. (Source: CNNMoney.com)

The Census Bureau on Tuesday released the 2007 American Community Survey, the government's annual estimates of social, economic and housing characteristics for the nation. Among the highlights: 25.3 - In minutes, the average commute to work in 2007, an increase from 25.0 minutes in 2006. (Source: Chicago Tribune)

Barack Obama leads John McCain, 49% to 44%, when registered voters are asked who they would vote for if the election were held today, according to the latest Gallup Poll Daily tracking update. (Source: Gallup)

All three of these are estimates based on samples. In fact, they're probably not correct, due to sampling error. Our goal in this chapter and the next is to characterize how close we think we are. In Section 8.1, we'll talk about sample means (the first two examples above), and in Section 8.2, we'll talk about proportions (the third example).

If you're ready to begin, just click on the "start" link below, or one of the section links on the left.